MESOSCALE PRECIPITATION DISCUSSION 0952
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
428 AM EST SAT DEC 23 2017

AREAS AFFECTED......NORTHEAST MS...NORTHERN AL...TN...KY...

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 230927Z - 231427Z

SUMMARY...ADDITIONAL SHOWERS AND EMBEDDED THUNDERSTORMS WILL
PRODUCE LOCALLY HEAVY RAINFALL EARLY THIS MORNING ACROSS AREAS
WITH LOW FLASH FLOOD GUIDANCE, THEREBY MAINTAINING THE THREAT FOR
FLASH FLOODING THROUGH 14Z.

DISCUSSION...THE LATEST MRMS LOOPS CONTINUE TO SHOW POCKETS OF
HOURLY RAINFALL RATES BETWEEN 0.50-1.00, WITH 3 HOURLY RATES NEAR
1.5 INCHES, ASSOCIATED WITH THE EXPANSIVE AREA OF SHOWERS AND
THUNDERSTORMS. INHIBITING HIGHER RATES CONTINUES TO BE THE
RELATIVE LACK OF DEEP-LAYER INSTABILITY, AS MUCAPES CONTINUE TO
REMAIN BELOW 500 J/KG PER THE LATEST SPC MESOANALYSIS. HELPING TO
OFFSET THE LIMITED CONVECTIVE CONTRIBUTION IS ROBUST SYNOPTIC
SCALE FORCING FOR DEEP LAYER ASCENT, OWING TO THE COUPLED UPPER
LEVEL DYNAMICS VIA NORTHERN AND SOUTHERN STREAM COMPONENTS.

THE VIGOROUS SOUTHERN STREAM WAVE CONTINUES TO SUPPLY RICH
MOISTURE TO THE OUTLOOK AREA, AS LOW-LEVEL SOUTHWESTERLY FLOW
50-55 KTS MAINTAINS HIGHLY ANOMALOUS LOW-LEVEL MOISTURE FLUX INTO
THE FRONTAL ZONE. IN ADDITION, THE LOW-LEVEL MOISTURE CONTRIBUTION
FORM THE WESTERN GULF OF MEXICO ALONG WITH THE SUBTROPICAL
CONNECTION ALOFT FROM SOUTH OF BAJA WILL FAVOR EQUALLY ANOMALOUS
PW VALUES AROUND 1.5 INCHES PRIOR TO THE FRONTAL PASSAGE.

PER THE LATEST HRRR TRENDS, SUPPORTED BY THE 00Z WRF-ARW AND AR2
GUIDANCE, 3 HOURLY RAINFALL RATES UP TO 1.5 INCHES WILL REMAIN
POSSIBLE THROUGH 14Z. THEREAFTER, THE MORE RAPID MOVEMENT OF THE
SOUTHERN STREAM SHORTWAVE WILL TOO RESULT IN AN SWIFTER EASTWARD
PROGRESSION OF THE STRONGER CELLS. GIVEN THE ANTECEDENT WET SOILS
FROM FRIDAY'S HEAVY RAINFALL, THESE POCKETS OF HEAVIER RAINFALL
MAY LEAD TO ADDITIONAL FLASH FLOODING.

HURLEY

ATTN...WFO...BMX...HUN...JKL...LMK...MEG...MRX...OHX...PAH...

ATTN...RFC...LMRFC...OHRFC...SERFC...

LAT...LON   38098480 37578369 36788345 35898420 35318534
            34318786 34208890 34868939 36448794 37588635